The invention relates to a method for applying a coating film to three-dimensionally curved surfaces of a dimensionally stable substrate and the coating films.
A process for coating three-dimensionally curved surfaces of dimensionally stable substrates with a coating film is known from patent document EP 361 351 A1. The coating film used there is formed by a supporting film, an adhesive layer, and a coating layer. Before applying the coating film, the radiation-curable coating layer is partially cured so that it is dust-dry. The coating film is then heated and drawn over the substrate that, if appropriate, has also been heated. After application of the coating film is complete, the coating layer is fully cured by thermal means. A hardening reaction between the adhesive layer, the coating layer, and the substrate may simultaneously occur.
In certain circumstances, different materials in a substrate must be coated independently. For example, transitions between sheet-metal components and plastic components on the body of a passenger car or in a motor vehicle interior are separately coated. This is because the high thermal loading conditions used for metals that are unsuitable for plastic. Unfortunately, the use of different coating films on different materials or surfaces may result in a different coating appearance.
Furthermore, the coating films have a supporting film which--when the supporting film is arranged centrally--remains on the product or--if the supporting film is arranged on the outside--is detached and if appropriate recycled following application of the coating film. In both cases, expenditure on the material is high, as a result of which the mass of the coating film to be used for coating and also the production costs are high.
An object of the invention is to provide better methods for applying coating films that are more universally applicable. Furthermore, an object of the invention is to provide a cost-effective coating film capable of being used in coating curved substrates.
The invention provides a method for coating a three-dimensionally curved surface of a dimensionally stable substrate. The method comprises applying a coating film to the substrate and subjecting the coating film to electromagnetic radiation below the visible spectrum. In addition, the invention provides a coating film comprising two layers: a coating layer having a partially cured, radiation-curable polymer; and an adhesive layer. The composition of the coating layer and the adhesive layer can be selected from the numerous polymeric coating and adhesive materials known in the art, such as those discussed in European patent document EP 0 361 351 and in the Concise Encyclopedia of Polymer Science and Engineering, Wiley Interscience, New York, both of which are specifically incorporated herein by reference.
In one embodiment, the coating film is heated to the glass transition temperature or slightly above the glass transition temperature of the polymer selected. The substrate can also be heated to that temperature. For example, the polymer of the coating layer can be selected as one having a glass transition temperature of below about 40.degree. C., or preferably below about 30.degree. C.
In other embodiments, the coating layer comprises a multi-layer structure having an outside layer comprising a fully cured clearcoat. The outside layer being the layer of the coating film that, after the coating film is applied to the substrate, is most external to the substrate or is in contact with the environment. The layers of the multi-layer structure may comprise numerous materials known in the art as appropriate for coating films. For example, a layer of the multi-layer structure can comprise a colored thermoplastic polymer material in the thermoplastic state. In addition or alternatively, the outside layer can comprises a fully cured thermosetting polymer and/or a binder material.
Numerous appropriate binder materials are known in the art and can be used in this invention. Preferred binder materials comprises one or more of the group consisting essentially of phosphazene, a phosphazene resin, a phosphazene derivative, a phosphazene intermediate, a urethane, a urethane derivative, a urethane intermediate, an acrylate, an acrylate derivative, and an acrylate intermediate.
In other embodiments, the method employs a coating film or coating film apparatus comprising a support base. The support base can be detached from the coating film, or vice versa, prior to applying the coating film to the substrate. The support base can be a film or a surface on which the coating layer, the adhesive layer, or a component of the coating film is stored. Also, the adhesive layer can be added to the coating film before the support base detaches from the coating film. Or, the adhesive layer can first be attached to the support base and thereafter the coating layer can be attached to the adhesive layer.
In other embodiments, the coating film contains a support base. Numerous support bases are known in the art and can be used in the invention. The adhesive layer and a pre-cured coating layer can be attached to a support base so that, for example, the coating layer is partially cured after being detached from the support base. Also, the coating layer can be partially cured while attached to a support base. In addition, the adhesive layer can be attached to the coating layer after the coating layer is detached from the support base.
In more detailed aspects, the substrate is subjected to at most a slight load by the full curing by means of the electromagnetic radiation within the claimed wave range. It should be noted here that if the coating layer is fully cured by means of electron beams, the wave image of the electron beams, i.e. with regard to their wavelengths, should be considered.
In particular, a coating film having only a coating layer and an adhesive layer is also beneficial since it is possible to dispense with the supporting film, which has hitherto been present and which is therefore no longer required. Thus, a supporting film arranged on the outside no longer has to be detached separately from the substrate.
In addition, the invention is explained in more detail with reference to exemplary embodiments illustrated in the figures. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention and when considered in conjunction with the accompanying drawings.